Scotland's ambulance service is set to introduce a priority despatch system following a National Audit Office finding that just one in three Glasgow ambulances reached a 999 incident within seven minutes, against a target of one in two.

The NAO report, published last week, identified the 'first come, first served' policy as one of the weaknesses in a system that is straining to cope with a 28 per cent increase in 999 calls in five years.

It urges the Scottish Ambulance Service to act urgently to consider prioritising life-threatening emergencies, and 'manage more systematically' the balance between demand, responsiveness and resources. The service considered - and rejected - priority despatch two years ago.

Although the response times achieved by the Scottish service generally compare favourably with other areas of Britain, there are wide variations in performance, with targets missed in remote rural areas and densely populated Glasgow and Lothian.

Glasgow's relatively poor performance, the report says, is related to managers' failure to motivate staff, a legacy of a dispute early this decade.

The introduction of priority despatch would bring Scotland into line with ambulance trusts in England, which have been instructed by the Department of Health to move to the new system by 2001.

An NAO spokesperson emphasised that priority despatch would need to be introduced with care, to avoid the risk of response times worsening during the transition period: 'We are not saying that priority despatch is the saviour for all of these problems, but we think there would be real benefits from it, particularly in Glasgow.'

The NAO report also recommends that the service and the Scottish Executive set and monitor performance measures to focus the development of the service.

Catriona Renfrew, director of commissioning at Greater Glasgow health board, said it had been working with the ambulance service for two years to improve standards and that 'they have improved'.

But she emphasised that the board was in no position to 'beat the service over the head' since the Scottish Ambulance Service is a special health board.

Scottish Ambulance Service chair Owen Clarke said standards had remained constant despite rising demand and low average running costs and management costs.

The Scottish Ambulance Service: a service for life. National Audit Office, 08547-023474.£12.10.